Proc logistic

[Frank_P]

Hi, could anyone explain to me why the classification results of the ctable statement in proc logistic are different from the ones that I calculate myself based on the outputted probability? The values are very similar, but I do not know why they are not equal? I use the greater equal as should be used for the ctable. Could it be related to the rounding?
Thanks for helping. Regards, Frank

[lvm]

According the the User's Guide, the probabilities obtained in the output window from the ctable option are rounded to the nearest 0.02. This would likely explain the differences you find for classification. Also, there is rounding when using the outroc= option (but different rounding than for the ctable output).
LVM

[Frank_P]

Thanks, that might indeed explain the differences. I could not spot that information myself, thanks again! Regards, Frank

[StatDave]

As mentioned in this usage note:

http://support.sas.com/kb/22596

the CTABLE results are based on bias-adjusted predicted probabilities not on the simple, unadjusted probabilities.